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The findings, which appeared in the American Journal of Gastroenterology, show that nurses participating in shift work, especially those working rotating shifts, face a significantly increased risk of developing IBS and abdominal pain compared to those working a standard daytime schedule.

“We know that people participating in shift work often complain of gastrointestinal symptoms such as abdominal pain, constipation and diarrhea,” said Sandra Hoogerwerf, M.D., assistant professor of internal medicine at the University of Michigan Medical School. “These are the same symptoms of IBS.”

IBS is the most common functional bowel disorder and is difficult to identify because it is diagnosed by clinical symptoms rather than tests, said Hoogerwerf, lead author of the study. IBS symptoms include recurrent episodes of abdominal pain or cramping in connection with altered bowel habits.

Hoogerwerf and her collegues evaluated nurses classified into three groups – 214 working permanent day shifts, 110 working permanent night shifts and 75 working rotating shifts between day and night – based on self-reported abdominal symptoms and sleep quality. More than 85 percent were women.

“Our findings suggest that nurses participating in shift work, particularly those who participate in rotating shift work, have a higher prevalence of IBS and abdominal pain. This association is independent of sleep quality,” the authors write.

“We know the colon has its own biological clock and that’s what increases the likelihood of having a bowel movement in the first 6 hours of the day,” Hoogerwerf says.

“Shift work can cause chronic disruption of that biological rhythm, resulting in that clock to constantly be thrown off and needing to adjust, creating symptoms of diarrhea, boating, constipation and abdominal pain and discomfort.”

The researchers said their study suggests that sleep disturbances do not completely explain the existence of IBS or abdominal pain associated with shift work.

“The question now for further research is if IBS and abdominal pain is an underlying manifestation of a circadian rhythm disorder,” Hoogerwerf says.

Meanwhile, the researchers suggest “practicing gastroenterologists should be aware of this association and educate patients with IBS on the possible impact of their work schedule on their symptoms.”